CHAMPAIGN – Energy costs at a Champaign school retrofitted with air-conditioning 10 years ago aren't much higher than at other schools, even though it operates year-round.
But costs vary greatly among the schools, depending on a building's use, district officials say.
At Kenwood Elementary, a year-round facility that was air-conditioned in 1995, energy costs total about 96 cents per square foot each year – including the summer months. That's 8 cents more than the average of 88 cents per square foot for the seven elementary schools without central air that are on a standard school calendar, said engineer Jim Gleason of GHR Engineers and Associates of Champaign. The difference is about $3,600 a year for a building Kenwood's size.
The school district tightly monitors air conditioning use at Kenwood, turning it off when students leave. And it's not used after hours or on weekends, said Gleason, whose firm works for the district's architect on newly proposed capital projects.
"We believe similar management of the other seven elementary schools will produce similar results," Gleason wrote in a letter Tuesday to Gene Logas, the district's chief financial officer.
At Barkstall and Stratton elementary schools, built in the late 1990s with central air, energy costs are much higher: about $1.92 a square foot, Logas said. But both were designed with oversized gyms and support areas that could be used by community groups after hours, Gleason said.
"Those buildings are used 365 days a year day and night," Logas said. "They're community resources with big gyms, but there's a cost: much higher electric and heating bills."
The proposed air-conditioning project would retrofit the other seven elementary schools with the same systems used at Kenwood, replacing the heating-only "unit-ventilators" in each classroom with new units cooled by a central chilled-water system. Each school would have digital-control features that weren't available when Kenwood was remodeled, Gleason said.
The retrofits won't involve replacing boilers, Gleason said, but the new digital controls will make the heating and cooling units much more efficient year-round, saving the district money. They also will have carbon dioxide sensors that will allow in only enough outside air to keep the indoor air fresh and avoid overventilating in winter or summer, he said.
"It's more precise, and it's tremendously more efficient," he said.
Some school district residents have suggested Champaign install window units in all the classrooms rather than paying for central air. Dr. Howard and Carrie Busey elementary schools have window units in all their rooms. And the remaining buildings without central air all have at least a few window units in administrative areas, said John Ayers Jr., assistant maintenance director for the district.
But window units pose several problems and tend to wear out in a few years, Gleason said.
At Dr. Howard, the PTA bought the window units, which were phased in between 1995 and 2004. But the district shouldered the cost of updating the wiring and running new electrical boxes to various rooms. At Carrie Busey, the district had to run new electrical service at a cost of more than $15,000, Ayers said.
Window units also create air quality problems. State regulations require schools to exchange the air inside the classroom frequently to cut down on carbon dioxide buildup, germs, mold and mildew. With window air-conditioners, which recirculate inside air, schools have to run the unit ventilators to bring in outside air, which is terribly inefficient, Gleason said.
"It's like leaving your refrigerator door open," he said. "They're canceling each other out."
Central air has much more efficient air-exchange systems.
At Carrie Busey and Dr. Howard, utility costs went up about 20 percent after the window units were installed, Ayers said, although that didn't account for rate increases. The district only allows them to run during school hours, but teachers in each room control the temperatures, officials said.
Don Fournier, an expert in energy and sustainability at the University of Illinois, suggested existing schools be fitted with a heat-pump heating and cooling system. One version of a conventional heat pump circulates water on a loop throughout the building, using a cooling tower or boiler to get the water to the right temperature. A geothermal heat pump circulates water down through the earth, which is about 55 degrees year-round, Fournier said.
Heat pumps are more expensive to install but "much cheaper to run," he said.
Fournier cited a real-life energy experiment in Lincoln, Neb. The school district built four 69,000-square-foot schools in 1995 – one with a heat pump, two with variable-air-volume systems and one with the more conventional constant-volume system – then monitored the energy use and costs.
The heat pump was the cheapest to operate and cost less up front than the variable-air systems that are also considered energy-efficient, he said. The conventional system was the cheapest up front but cost the most to operate.
Gleason said both the retrofit systems used at Kenwood and the new systems at Barkstall and Kenwood are variable-air-volume systems. The district is considering heat pumps, along with other environmentally friendly systems, for the new schools that would be built if voters approve the projects, Gleason said.